Update "ethitter.com" references to remove unnecessary redirects
More coding standards tweaks
Note why the plugin class, which is a singleton, also populates a global variable.
Readme updates for 2.1
Support string notation for plugin options, in addition to preferred array notation.

WP has set the expectation that arguments can be specified as strings joined by ampersands. While I think it's an unnecessarily-confusing way of specifying arguments, some users seem to like it.

See http://wordpress.org/support/topic/unable-to-customise-plugin-behaviour-in-non-widget-implementation.
Allow plugins to filter the dropdown and its components.

Fixes #1.
More readme updates for v2.1.